This invention generally relates to housings for electrical apparatus and has particular utility as an improved housing for an ionization detector array of a tomographic X-ray scanner.
By way of background, tomographic X-ray scanners enable a medical practitioner to non-invasively obtain detailed information relative to the location and condition of organs and other tissues within a patient's body, such information taking the form of a radiographic image of a thin cross-section or "slice" of the area of the body under consideration.
In the computer-assisted tomographic process, a narrow X-ray or gamma ray beam is transmitted transversely through a section of the patient anatomy and the emerging beam is detected by high-efficiency radiation detectors. A series of individual measurements of the transmitted radiation is made about the subject so as to obtain multiple views of the "slice" in question. By virtue of these views, large amounts of information and data are acquired as to the differences in radiological contrast of the cross-section in question. This data, constituting individual measurements at many angles about the subject, then provides the input from which X-ray or gamma ray attenuation coefficients can be calculated in a computer and the image of the cross-section of the patient anatomy actually reconstructed. Thus, a computer-assisted tomographic scanner obtains, by mathematical reconstruction, a transverse sectional image from transmitted radiation projection data, all as is well known.
A typical apparatus utilized in the tomographic process as above described can be seen by initial reference to FIG. 1 of the appended drawings. A closely collimated X-ray source 10 is designed to ideally deliver a very narrow beam or beams of photons 12 through a "slice" 14 in an object 16 which typically is the torso or head of the patient. A multi-channel radiation detector 18 is disposed opposite the collimated X-ray source so as to receive the beam or beams of photon 12 passing through the slice 14 of interest, all while the collimated X-ray source 10, and the detector 18 in this example, undergo relative motion with respect to the patient, i.e. rotational motion in this example.
During the rotation of the source and detector, each detector element which constitutes adjacent pairs of the electrode plates 20, forms a data channel and responds to the beam from the collimated X-ray source. Considering the rotational movement, however, each detector element obtains a different and discrete data set relative to the amount of attenuation of the X-ray beam passing edgewise through the plane of interest 14. This information then is fed to a conventional non-illustrated external signal processing circuit including a computer whereat, through well-known mathematical algorithms, the image through the plane of interest or cross-sectional slice 14 of the patient is reconstructed.
The multi-channel radiation detector 18 typically comprises a plurality of stacked or spaced-apart electrode plates 20 which are disposed as shown in an elongated chamber 22 which is filled with a pressurized ionizable gas. It is necessary, of course, to extract signals generated by each of the electrode plates 20 to the exterior of the elongated housing 22 for connection to the signal processing circuits as described. In this respect difficulties have been encountered in the prior art in effecting the so-called "feedthrough" of the electrical connections from the interior of the elongated detector chamber to the exterior thereof.
For example, radiation detectors in this environment typically have hundreds of closely-spaced electrode plate pairs, with each electrode plate requiring an electrical connection thereto. Very finely machined "feedthroughs" such as schematically indicated at reference numeral 24 typically are provided. The precision machining necessary to generate so many closely spaced feedthroughs markedly raises the cost of the resulting detector structure. Considering that the detector array is disposed in a pressurized ionizable gas, the possibility of gas leakage due to the provision of so many connector feedthroughs is increased. Further, and recognizing the inherent sensitivity of the low-magnitude signal extraction from the electrode plates, the many individual connectors needed to effect the electrical coupling, the varying distances between the individual connector wires, and the resulting changes in inter-connector capacitance, oftentimes combined to create signal perturbations which resulted in measurement errors.
Notwithstanding such problems as are associated with the feedthrough of the electrical conductors to the detector array disposed within the sealed chamber, no other means of effecting the necessary connections were recognized to exist.